1/* 2 * A fast checksum routine using movem 3 * Copyright (c) 1998-2007 Axis Communications AB 4 * 5 * csum_partial(const unsigned char * buff, int len, unsigned int sum) 6 */ 7 8 .globl csum_partial 9csum_partial: 10 11 ;; r10 - src 12 ;; r11 - length 13 ;; r12 - checksum 14 15 ;; Optimized for large packets 16 subq 10*4, $r11 17 blt _word_loop 18 move.d $r11, $acr 19 20 subq 9*4,$sp 21 clearf c 22 movem $r8,[$sp] 23 24 ;; do a movem checksum 25 26_mloop: movem [$r10+],$r9 ; read 10 longwords 27 ;; Loop count without touching the c flag. 28 addoq -10*4, $acr, $acr 29 ;; perform dword checksumming on the 10 longwords 30 31 addc $r0,$r12 32 addc $r1,$r12 33 addc $r2,$r12 34 addc $r3,$r12 35 addc $r4,$r12 36 addc $r5,$r12 37 addc $r6,$r12 38 addc $r7,$r12 39 addc $r8,$r12 40 addc $r9,$r12 41 42 ;; test $acr without trashing carry. 43 move.d $acr, $acr 44 bpl _mloop 45 ;; r11 <= acr is not really needed in the mloop, just using the dslot 46 ;; to prepare for what is needed after mloop. 47 move.d $acr, $r11 48 49 ;; fold the last carry into r13 50 addc 0, $r12 51 movem [$sp+],$r8 ; restore regs 52 53_word_loop: 54 addq 10*4,$r11 ; compensate for last loop underflowing length 55 56 moveq -1,$r9 ; put 0xffff in r9, faster than move.d 0xffff,r9 57 lsrq 16,$r9 58 59 move.d $r12,$r13 60 lsrq 16,$r13 ; r13 = checksum >> 16 61 and.d $r9,$r12 ; checksum = checksum & 0xffff 62 63_no_fold: 64 subq 2,$r11 65 blt _no_words 66 add.d $r13,$r12 ; checksum += r13 67 68 ;; checksum the rest of the words 69_wloop: subq 2,$r11 70 bge _wloop 71 addu.w [$r10+],$r12 72 73_no_words: 74 addq 2,$r11 75 ;; see if we have one odd byte more 76 bne _do_byte 77 nop 78 ret 79 move.d $r12,$r10 80 81_do_byte: 82 ;; copy and checksum the last byte 83 addu.b [$r10],$r12 84 ret 85 move.d $r12,$r10 86